Plug-in Hybrid Electric Vehicles are propelled, depending on operating conditions, by either an electric motor or an internal combustion engine. An onboard battery is recharged either through the electric motor, which acts as a generator when the vehicle is slowing down, or through an onboard charging system that is plugged into the power grid by the operator when the vehicle is not in use.
A fuel vapor recovery system, which includes a fuel vapor canister, is coupled to the fuel tank to absorb fuel vapors which otherwise may be emitted to the atmosphere. When the internal combustion engine is operating, fuel vapors are desorbed from the canister and purged into the engine for combustion.
Plug-in Hybrid Electric Vehicles may be powered by the battery for long periods of time and vapors from the fuel tank may be infrequently purged into the engine for combustion. To prevent vapor emissions from the canister into the atmosphere under these conditions, the fuel tank is often sealed and not vented to atmosphere. Further, plastic fuel tanks are frequently utilized in PHEVs for their lighter weight, which improves fuel economy.
The inventors herein have recognized that new plastic fuel tanks may expand with age when fuel vapors chemically combine with the plastic tank. Depending on the operators driving habits, some PHEVs may infrequently use gasoline and the aging process may be prolonged.
Thus, the inventors herein have developed systems and methods to at least partially address the above issues. In one example the issues described above may be addressed by a method for a plug-in hybrid vehicle which comprises the following: during a plug-in event to recharge a battery of the vehicle, isolating a plastic fuel tank from both an internal combustion engine of the vehicle and from atmosphere; and operating a fuel pump coupled to the plastic fuel tank during each of a plurality of the plug-in events until the plastic fuel tank becomes aged to a predetermined degree by fuel vapors generated therein. In this manner, the fuel tank is aged more rapidly than would otherwise occur resulting in more accurate fuel level readings and less noise and vibration than heretofore possible.
In another example, the plastic fuel tank aging is directly related to temperature of fuel in the plastic fuel tank and the operating time of the fuel pump during the plug-in events. In another example, the plastic fuel tank aging is related to pressure in the plastic fuel tank during the plug-in events and the fuel pump is shut off when pressure in the plastic fuel tank reaches a preset pressure.
In still another example, a method for a plug-in hybrid vehicle, comprises: estimating aging of a plastic fuel tank which supplies fuel to a combustion engine of the vehicle in relation how much time the fuel tank is at a fuel level over a preset level and fuel temperature during those times; during plug-in events in which a battery of the vehicle is recharged from the power grid, sealing a plastic fuel tank which is coupled to an engine of the vehicle so that the plastic fuel tank is isolated from both the engine and from atmosphere; operating a fuel pump coupled to the plastic fuel tank during each of the plug-in events; estimating aging of the tank during each of the plug-in events and generating a total aging estimate from both filling the plastic fuel tank over the preset level and operating the fuel pump during the plug-in events; and stopping operation of the fuel pump during the plug-in events when the total aging estimate reaches the desired aging estimate.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.